Dense Seed Layer and Method of Formation

ABSTRACT

A semiconductor device includes a workpiece and a first material layer disposed over the workpiece. The first material layer has a first number of atoms at a surface. A seed layer is disposed over the first material layer. The seed layer includes a chemisorbed monolayer of a second number of atoms at the surface having a surface coverage of at least 0.5 such that the ratio of the number of first atoms at the surface to the number of second atoms at the surface is no more than 2:1. The second atoms of the seed layer include oxygen or nitrogen.

This application is a divisional of patent application Ser. No.12/467,065, filed May 15, 2009 and now U.S. Pat. No. x,xxx,xxx, which isa divisional of patent application Ser. No. 11/865,886, filed on Oct. 2,2007 and now U.S. Pat. No. 7,576,005, which is a divisional of patentapplication Ser. No. 10/980,561, filed on Nov. 3, 2004 and now U.S. Pat.No. 7,294,851. All of these application are incorporated herein byreference.

TECHNICAL FIELD

The present invention relates generally to the fabrication ofsemiconductors, and more particularly to methods of forming seed layersof semiconductor devices.

BACKGROUND

Semiconductor devices are used in a variety of electronic applications,such as computers, cellular phones, personal computing devices, and manyother applications. Home, industrial, and automotive devices that in thepast comprised only mechanical components now have electronic parts thatrequire semiconductor devices, for example.

Semiconductor devices are manufactured by depositing many differenttypes of material layers over a semiconductor workpiece or wafer, andpatterning the various material layers using lithography. The materiallayers typically comprise thin films of conductive, semiconductive, andinsulating materials that are patterned and etched to form integratedcircuits (IC's). There may be a plurality of transistors, memorydevices, switches, conductive lines, diodes, capacitors, logic circuits,and other electronic components formed on a single die or chip.

With the semiconductor industry targeting smaller feature sizes, theinterface regions between two adjacent thin films, and the surfaceproperties of thin films, have become more important to deviceperformance. The definition of an interface region between two films interms of the thickness of the interface region, i.e., the number ofatomic layers or molecular layers the interface region comprises, hasbecome more critical as semiconductor devices are scaled down in size.In addition, there are limitations to the maximum temperatures allowedin thin film deposition processes because of device performancedegradation.

In order to improve the interface region between two adjacent thinfilms, seed layers are often used. FIG. 1 shows a cross-sectional viewof a prior art semiconductor device 100 comprising a workpiece 102. Theworkpiece 102 may comprise a semiconductor wafer, and may include avariety of material layers formed thereon, for example, metal layers,semiconducting layers, dielectric layers, diffusion barrier layers,etc., not shown. A first material layer comprising a metal layer 104 isformed over the workpiece 102, as shown. The metal layer 104 maycomprise a gate of a transistor, a plate of a capacitor, a conductiveline, or other electrical components or portions of electricalcomponents of an integrated circuit, for example.

In many semiconductor designs, it is desirable to form a second materiallayer comprising an insulating or semiconductor material layer 114 overthe metal layer 104. During the formation of the second material layer114, an interface region 112 can form between the metal layer 104 andthe insulating or semiconductor material layer 114, often comprisingmaterial of both the metal layer and the insulating or semiconductormaterial layer 114, for example. In some applications, this isundesirable, because the interface region 112 has a detrimental impacton the performance of the semiconductor device 100. It is the goal inmany semiconductor designs to form an insulating or semiconductormaterial layer 114 directly abutting the metal layer 104, so that thebulk properties of the insulating or semiconductor material layer 114and the metal layer 104 are achieved. Thus, often a seed layer 110 isformed on the metal layer 114 before depositing the material layer 114,as shown, to decrease the interface region 112 thickness.

One method of forming the seed layer 110 is by forming a monolayer ofthe atoms 108 of a desired species by chemisorption. Chemisorption is aprocess whereby an atom or molecule adheres to a surface through theformation of a chemical bond, rather than by physisorption. Inphysisorption, an atom or molecule adheres to a surface by a van derWaals type force or electrostatic attraction rather than by a chemicalbond. Generally, chemisorption produces stronger bonds thanphysisorption.

A problem with forming a seed layer 110 comprising a monolayer of atoms108 is that there is a limitation on the number of atoms 108 that may beformed on the top surface of the metal layer 104. This is because manyof the atomic species that are important in semiconductor manufacturingabsorb from the gas phase onto a metal surface by dissociativeadsorption. In this process of dissociative adsorption, the first stepis the adsorption of the molecule (like O₂ or N₂) on the surface ofmetal layer 104, and the second step is the dissociation of the moleculewith each of the atoms 108 now being bound individually to the surfaceof metal layer 104. After a sufficient number of atoms 108 is adsorbedon the surface of metal layer 104 it becomes impossible for additionalmolecules from the gas phase to get close enough to the metal surface104 to start the dissociative adsorption process, and the moleculesbounce back from the surface. After access to the metal layer 104surface is blocked in this way, the saturation coverage for theatomic/molecular species (e.g., of atoms 108) is reached. Typically thesaturation coverage is well below one monolayer, i.e., where there wouldbe a 1:1 relationship between atoms 106 and 108. For example, an idealmonolayer would have for each metal atom 106 in the metal layer 104surface, one oxygen or nitrogen atom 108 adsorbed on the metal layer 104surface.

However, a 1:1 monolayer is not actually formed; typical saturationcoverages are well below 0.4 and often not more than 0.25 monolayer,which occurs because of a limited number of adsorption sites. The metallayer 104 has a number of atoms 106 disposed at the top surface. Theatoms 106 at the top surface of the metal layer 104 have a fixed numberof adsorption sites that may be occupied if adsorption of atoms 108 ofthe seed layer 110 proceeds via dissociative adsorption of molecules outof a gas phase, which is typically the process used to form the seedlayer 110. For example, if the metal layer 104 comprises ruthenium (Ru)with crystal orientation 001, i.e., Ru (001), and atomic oxygen is thespecies to be formed as a seed on the metal layer 104, a seed layer 110of a monolayer of oxygen atoms 108 having a density of 0.25 or less isachieved when the seed layer 110 is formed at room temperature byadsorption from a gas phase of molecular oxygen. In particular, in thisexample, there may be one oxygen atom 108 in the monolayer seed layer110 for every four atoms 106 of the metal element of the material layer104, as shown, resulting in a 1:4 ratio of the seed layer 110 atoms tothe metal layer 104 atoms, or a seed layer 110 having density of 0.25 orless with respect to the density of the metal layer 104.

When the next material layer 114 is deposited, an interface region 112is formed, comprising a thickness d₁ of about 10 to 15 atomic layers. Itis desirable for the interface region 112 to be as thin as possible, ormore preferably, for no interface region 112 to form, in someapplications.

What is needed in the art is a method of forming a material layer 114over a metal layer 104 that results in the formation of a thinnerinterface region 112 between the material layer 114 and the metal layer104. A well-defined interface between a metal layer 104 and asubsequently deposited material layer 114 is needed.

What is also needed in the art are improved methods of forming seedlayers, in order to overcome the current limitations of interface andthin film engineering, and the limitations of kinetics of interfaceformation and thin film growth.

SUMMARY OF THE INVENTION

These and other problems are generally solved or circumvented, andtechnical advantages are generally achieved, by preferred embodiments ofthe present invention, which provide methods of forming dense seedlayers and structures thereof. Seed layers comprising a monolayer ofatoms having a density of about 0.5 monolayer or greater may bemanufactured over a metal layer, resulting in a well defined interfaceregion between the metal layer and a subsequently formed material layer.

In accordance with a preferred embodiment of the present invention, amethod of forming a seed layer on a material layer of a semiconductordevice includes adsorbing a monolayer of first atoms on the materiallayer, the first atoms comprising a first density, lowering thetemperature of the semiconductor device, and forming thin film of weaklybound physisorbed layers of first molecules over the monolayer. Thephysisorbed thin film of first molecules is exposed to energy,dissociating a portion of the first molecules in the weakly bound layerproximate to the monolayer of first atoms. The semiconductor device isheated, wherein heating the semiconductor device comprises migrating thedissociated first molecules in the weakly bound layers closest to thefirst atomic monolayer into the monolayer of first atoms and removingthe remainder of the physisorbed weakly bound layer of first molecules.The first atoms of the monolayer comprise a second density after heatingthe semiconductor device, the second density being greater than thefirst density, wherein the monolayer of first atoms comprises the seedlayer.

In accordance with another preferred embodiment of the presentinvention, a method of manufacturing a semiconductor device includesproviding a workpiece, forming a material layer over the workpiece, andforming a seed layer over the material layer by chemisorption. The seedlayer comprises a monolayer of first atoms and a first density. Themethod includes lowering the temperature of the workpiece, forming aphysisorbed layer over the seed layer, the physisorbed layer comprisinga weakly bound layer of first molecules, and dissociating a portion ofthe first molecules in the physisorbed layer, producing atoms from firstmolecules being proximate the seed layer. The workpiece is heated,causing integration of the atoms from the dissociated first molecules ofthe physisorbed layer into the seed layer and removing the physisorbedlayer. The integration of the atoms from the dissociated first moleculesinto the seed layer increases the density of the seed layer to a seconddensity, the second density being greater than the first density.

In accordance with another preferred embodiment of the presentinvention, a semiconductor device includes a workpiece, a first materiallayer disposed over the workpiece, the first material layer comprisingfirst atoms having a first density, and a seed layer disposed over thefirst material layer. The seed layer comprises a chemisorbed monolayerof second atoms, the second atoms of the seed layer comprising a seconddensity. The second density is about 0.5 or greater relative to thefirst density of the first molecules of the first material layer.

Advantages of preferred embodiments of the present invention includeproviding a thinner interface region between a material layer and asubsequently deposited material layer. The seed layer described hereinis very dense and thus provides an improved surface for the formation ofa subsequent material layer, resulting in a well-defined, thinner,interface region.

The foregoing has outlined rather broadly the features and technicaladvantages of embodiments of the present invention in order that thedetailed description of the invention that follows may be betterunderstood. Additional features and advantages of embodiments of theinvention will be described hereinafter, which form the subject of theclaims of the invention. It should be appreciated by those skilled inthe art that the conception and specific embodiments disclosed may bereadily utilized as a basis for modifying or designing other structuresor processes for carrying out the same purposes of the presentinvention. It should also be realized by those skilled in the art thatsuch equivalent constructions do not depart from the spirit and scope ofthe invention as set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a cross-sectional view of a prior art semiconductor devicehaving a monolayer seed layer with a low density, and a thick interfaceregion formed between a metal layer and a subsequently formed materiallayer;

FIGS. 2 through 6 show cross-sectional views of a method of forming adense monolayer seed layer on a semiconductor device at various stagesof manufacturing in accordance with an embodiment of the presentinvention; and

FIG. 7 shows a material layer formed over a metal layer having a densemonolayer seed layer formed thereon in accordance with an embodiment ofthe present invention, wherein a thinner interface region is formedbetween the material layer and the metal layer.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the preferredembodiments and are not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the presently preferred embodiments arediscussed in detail below. It should be appreciated, however, that thepresent invention provides many applicable inventive concepts that canbe embodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the invention, and do not limit the scope of the invention.

The present invention will be described with respect to preferredembodiments in a specific context, namely the formation of a monolayerseed layer on a metal layer. The invention may also be applied, however,to the formation of a monolayer seed layer on other material layers,such as semiconductive materials or insulating materials, as examples.

Prior art methods of forming seed layers result in the formation of lowdensity seed layers, as previously described herein with reference toFIG. 1. The surface coverage of a material layer that can be achievedfor chemisorbed atoms, e.g., oxygen or nitrogen, is limited by theadsorption sites on the material that are available to be occupied ifadsorption of molecules proceeds by dissociative adsorption of moleculesout of the gas phase.

Embodiments of the present invention achieve technical advantages byovercoming this limitation in the number of adsorption sites byimplementing process steps that allow for adsorption of additionalmolecules generated in a physisorbed layer of molecules that is formedon top of the chemisorbed layer. Preferred embodiments of process stepsthat may be used to generate a chemisorbed monolayer of significantlyhigher two-dimensional density, e.g., as viewed in a cross-sectionalview in FIGS. 6 and 7, than is possible by dissociative adsorptionpurely out of the gas phase, will next be described. Embodiments of thepresent invention comprise processes of forming very dense seed layersfor thin film growth, which is particularly beneficial for oxidation andnitridation processes; e.g., in the formation of oxide layers, nitridelayers, and oxynitride layers.

Referring to FIG. 2, a cross-sectional view of a semiconductor device200 is shown. The semiconductor device 200 includes a workpiece 202. Theworkpiece 202 may include a semiconductor substrate comprising siliconor other semiconductor materials covered by an insulating layer, forexample. The workpiece 202 may also include other active components orcircuits formed in a front end of line (FEOL), not shown. The workpiece202 may comprise silicon oxide over single-crystal silicon, for example.The workpiece 202 may include other conductive layers or othersemiconductor elements, e.g. transistors, diodes, etc. Compoundsemiconductors, GaAs, InP, Si/Ge, or SiC, as examples, may be used inplace of silicon. For example, the workpiece 202 may include componentregions or various circuit elements formed therein. The workpiece 202may include a variety of material layers formed thereon, for example,metal layers, semiconducting layers, dielectric layers, diffusionbarrier layers, etc., not shown.

A material layer 204 is formed over the workpiece 202. The materiallayer 204 may comprise conductive, insulative, or semiconductivematerials, for example. In one embodiment of the invention, the materiallayer 204 preferably comprises a metal. The material layer 204 is alsoreferred to herein as a metal layer 204. The metal layer 204 preferablycomprises conductive materials typically used in semiconductormanufacturing, such as copper (Cu), aluminum (Al), refractory metalssuch as tantalum (Ta), titanium (Ti), tungsten (W), ruthenium (Ru), ormolybdenum (Mo), magnetic materials such as niobium (Nb), gadolinium(Gd), dysprosium (Dy), cobalt (Co), or combinations or alloys thereof,as examples, although alternatively, the metal layer 204 may compriseother materials. The metal layer 204 may comprise a thickness of about100 nm or greater, for example, although alternatively, the metal layer204 may comprise other dimensions. The metal layer 204 may have beenpreviously patterned using lithography, or the metal layer 204 may bepatterned in subsequent manufacturing process steps (not shown).

The metal layer 204 is comprised of a plurality of atoms 206. The atoms206 at the top surface of the metal layer 204 comprise a first density.The atoms 206 of the metal layer 204 are also referred to herein asfirst atoms.

The workpiece 202 is exposed to a gas, preferably at room temperature,for example, although alternatively other temperatures may be used. Thegas contains a desired elemental species that will be formed on themetal layer 204 as a seed layer. For example, the gas may compriseoxygen, nitrogen, or combinations thereof, as examples, althoughalternatively, other elements may be used.

The incoming molecules 208 a of the gas comprise the atomic species tobe adsorbed on the metal layer 204. The atoms of the incoming molecules208 a are bound to one another by a chemical bond 216, as shown. Forsimple diatomic molecules like oxygen and nitrogen, there is onechemical bond binding two atoms of the same atomic species (O₂, N₂). Thetop surface of the metal layer 204 comprises a first number ofadsorption sites accessible by dissociative adsorption of the molecules208 a of the gas out of a gas phase. Thus, when introduced to the gas,some of the molecules 208 a of the gas are adsorbed on the surface ofmetal layer 204, where they immediately dissociate and form chemisorbedatoms 208 b on the surface of the metal layer 204.

When the molecules 208 a reach the top surface of the metal layer 204,dissociative adsorption of some of the molecules 208 a occurs, breakingthe chemical bond 216 between the two atoms of a molecule 208 a, asshown in phantom at region 218, forming chemisorbed atoms 208 b thathave a strong chemical bond with atoms 206 of the top surface of themetal layer 204. A monolayer of chemisorbed atoms 208 b is formed overthe metal layer 204. The monolayer of chemisorbed atoms 208 b comprisesa seed layer 210 having a low density at this point of the manufacturingprocess, wherein the density is limited by the number of adsorptionsites of the top surface of the metal layer 204 that are accessible tothe normal process of dissociative adsorption (such as for O₂ and N₂).The density of the seed layer 210 at this point in the manufacturingprocess is also referred to herein as a first density.

Thus, the incoming molecules 208 a dissociate on the surface of themetal layer 204, and a seed layer 210 comprising a monolayer ofchemisorbed atoms 208 b is formed. At a certain atomic coverage, inparticular, the saturation coverage, additional dissociative adsorptionis blocked, because the incoming molecules 208 a cannot reach thesurface of the metal layer 204 any longer. After the adsorption sites ofthe top surface of the metal layer 204 are filled, the metal layer 204top surface is blocked from additional dissociative adsorption byinteraction with the previously adsorbed chemisorbed atoms 208 b.

After the limited number of atoms 208 b are chemisorbed to the metallayer 204 top surface, the temperature of the workpiece 202, and alsopreferably, the temperature of the gas containing the incoming molecules208 a, is lowered. The temperature is preferably lowered to atemperature lower than a desorption temperature for the seed layer 210comprising the chemisorbed atoms 208 b around the condensationtemperature for the gas, in one embodiment. The temperature ispreferably lowered to about 31 degrees K or greater for O₂ and about 26K or greater for N₂, as examples, although the temperature may also belowered to other temperatures.

At low temperatures, when the gas containing the molecules isintroduced, a thick layer of condensed molecules is adsorbed on top ofthe chemisorbed layer 210 of molecules, forming a physisorbed layer 220of physisorbed molecules 208 a, as shown in FIG. 3. Note that themolecules labeled 208 a in FIGS. 3, 4 and 5 represent physisorbedmolecules, whereas molecules labeled 208 a in FIG. 2 present incomingmolecules.

In contrast to the strongly bound chemisorbed atoms 208 b on the surfaceof the metal layer 204, the binding forces of the molecules 208 a of thephysisorbed layer 220 are relatively weak, and typically comprise vander Waals type bonds, for example. The physisorbed layer 220 maycomprise a molecular condensate or molecular crystal, for example, inone embodiment. The physisorbed layer 220 preferably comprises multiplelayers of monolayers of the physisorbed molecules 208 a, and maycomprise two or more monolayers of the physisorbed molecules 208 a, forexample.

In one embodiment, when the temperature of the workpiece 202 is lowered,the temperature of the gas containing the incoming molecules 208 a isalso lowered. Alternatively, the temperature of the gas may not beincreased, for example. The incoming molecules 208 a of FIG. 2 have a“sticking” probability of the incoming molecules 208 a, i.e., not everymolecule 208 a of FIG. 2 from the gas phase may adsorb long enough inthe molecular precursor state so that there is sufficient time enough todissociate the molecule 208 a and have successful dissociativeadsorption. If the incoming gas is cooled, the incoming molecules 208 aof FIG. 2 have less energy and are more likely to stay long enough onthe surface to dissociate, for example.

Referring again to FIG. 3, in one embodiment, the physisorbed layer 220comprises about two to five monolayers of physisorbed molecules 208 a.In another embodiment, the physisorbed layer 220 comprises about 20 to30 monolayers of physisorbed molecules 208 a, to be described furtherherein. The physisorbed layer 220 comprises a thickness h₁, as shown inFIG. 4.

Next, preferably while the workpiece 202 is kept at the low temperature,a beam of energy 224 is used to irradiate the physisorbed layer 220, tocause dissociation of a portion of the molecules 208 a of thephysisorbed layer 220, as shown in FIG. 4. The beam of energy 224preferably comprises energetic particles or radiation, e.g., electrons,ions, neutral particles, or electromagnetic radiation or ultravioletlight, as examples, although alternatively, the energy may compriseother forms of energy that can break molecular bonds in the physisorbedlayer 220. A portion of the physisorbed molecules 208 a in thephysisorbed layer 220 are desorbed, shown at 208 c, from the weaklybound physisorbed condensate or molecular crystal 220, simultaneouslywhile molecules 208 d within the bulk of the physisorbed layer 220 aredissociated. Some of the dissociated molecules 208 d of the physisorbedlayer 220 in region 226 at the bottom of the physisorbed layer 220 areclose to the top surface of the seed layer 210, as shown. As a portionof the physisorbed molecules 208 a are dissociated, forming dissociatedmolecules 208 d within the physisorbed layer 220, a portion of thephysisorbed molecules 208 a desorbs and leaves the physisorbed layer220, as shown at 208 c, decreasing the thickness of the physisorbedlayer 220 to a thickness h₂, as shown in FIG. 5, wherein h₂ is less thanh₁, for example.

Next, the remaining physisorbed layer 220 is thermally desorbed byheating the workpiece 202, e.g., by returning the workpiece 202 to roomtemperature, although alternatively, other temperatures may be used.During this process, the atoms of the dissociated molecules 208 dgenerated at the bottom of the physisorbed layer 220 proximate themonolayer seed layer 210 migrate to adsorption sites between theadsorption sites already occupied by the chemisorbed atoms 208 bmonolayer seed layer 210, as shown in FIG. 6 as chemisorbed atoms 208 e.Without the novel processing steps of lowering the temperature, exposingthe physisorbed layer 220 to energy that breaks molecular bonds in thephysisorbed layer 220, and then raising the temperature of the workpiece202, the additional adsorption sites adapted to bond to the atoms 208 ein the seed layer 230 generated form dissociated molecules 208 d wouldnot be accessible for dissociative adsorption out of a gas phase, forexample.

Thus, the novel physisorbed layer 220 comprising a solid phase formedadjacent and abutting the seed layer 210 makes additional adsorptionsites available in the metal layer 204 for bonding to the atoms 208 e inthe seed layer 230, resulting in a seed layer 230 with a significantlyhigher two-dimensional density of atoms 208 b and 208 e. The resultingseed layer 230 comprises a much more dense chemisorbed monolayer seedlayer 230 with adsorption sites occupied by atoms 208 e from dissociatedmolecules 208 d from a physisorbed layer 220 comprising a solid phase:adsorption sites that would not have been accessible via dissociativeadsorption out of a gas phase.

The seed layer 230 comprises a second density that is greater than thefirst density of the seed layer 210. The second density of preferably atleast two times the first density of the seed layer 210, in oneembodiment.

The density of the resulting seed layer 230 is preferably at least 0.5times the density of the metal layer 204. For example, if the metallayer 204 comprises atoms 206 comprising a first density, and the seedlayer 230 comprises atoms 208 b and 208 e comprising a second density,the seed layer 230 preferably comprises a second density of about 0.5 orgreater relative to the first density of the first molecules of thefirst material layer. In one embodiment, the second density of the atoms208 b and 208 e of the seed layer 230 comprises about 0.67 or greaterrelative to the first density of the atoms 206 of the metal layer 204,as shown in FIG. 6, where there are two atoms 208 b and 208 e of themonolayer seed layer 230 for every three atoms 206 at the top surface ofthe metal layer 204, a ratio of 2:3, or a density of about 0.67.

In another embodiment, the metal layer 204 top surface comprises a firstnumber of adsorption sites accessible by dissociative adsorption ofmolecule 208 a out of a gas phase, and the atoms 208 b and 208 e of theseed layer 230 occupies a second number of adsorption sites of the topsurface of the metal layer 204, wherein the second number is greaterthan the first number. The second number of adsorption sites is at leasttwo times the first number of adsorption sites, in one embodiment.

The novel process of forming a seed layer 230 described herein enablesthe formation of an atomic species 208 e, e.g., atoms 208 d fromdissociated molecules 208 d of the physisorbed layer 220 shown in FIG.5, close to the surface of the seed layer 210 having a previously fullyadsorbed chemisorbed, e.g., atoms 208 b of monolayer 210 of the species.The atoms 208 d generated by dissociation are entrapped in thephysisorbed layer 220, and upon thermal desorption of the physisorbedlayer 220, the atoms 208 e from the dissociated molecules find their wayinto adsorption sites in the top surface of the metal layer 204 notaccessible to dissociative adsorption out of the gas phase.

A material layer 234 is then formed over the seed layer 230, as shown inFIG. 7. The material layer 234 is also referred to herein as a secondmaterial layer 234. The material layer 234 preferably comprises O, N, anO-containing material, or an N-containing material, as examples,although alternatively, the material layer 234 may comprise othermaterials. The material layer 234 may comprise a thickness of about 100nm or greater, for example, although alternatively, the material layer234 may comprise other dimensions. An interface region 232 may be formedbetween the seed layer 230 and the material layer 234. If present, theinterface region 232 is thin, comprising a thickness of a few atomiclayers or a few nm or less, for example, and is well defined, e.g., theproperties and thickness of the interface region 232 are predictable andrepeatable.

In accordance with embodiments of the present invention, the steps oflowering the temperature, forming the physisorbed layer 220, irradiatingthe physisorbed layer 220 with energy 224, and heating the workpiece 202to adsorb the atoms 208 e from dissociated molecules 208 d of thephysisorbed layer 220 into the seed layer 230 and remove the physisorbedlayer 220, may be repeated several times to obtain the maximum atomiccoverage possible of the metal layer 204, i.e., until no more atoms 208e can be chemisorbed on the surface of the metal layer 204, because allpossible adsorption sites are occupied. The novel manufacturing processmay be repeated two or more times to increase the density of the seedlayer 230, while the lateral interaction between neighboring adsorbedatoms 208 b and 208 e in the seed layer 230 continue to permit furtheradsorption. The process may be optimized with respect to temperature andthe number of times these steps are repeated in order to generate thehighest possible coverage and density of the seed layer 230 atoms 208 band 208 e.

For example, in one embodiment, preferably the physisorbed layer 220comprises about 20 to 30 monolayers of the physisorbed molecule 208 a.In this embodiment, very low temperatures are needed to generate thecondensate. The temperature may need to be lowered to about 31 degrees Kor greater for O₂ and about 26 K or greater for N₂, as examples. Such athick physisorbed layer 220 is advantageous in that the maximum coverageof chemisorbed atoms 208 e within the seed layer 230 may be achieved inone or two process runs, i.e., the steps of lowering the temperature,forming the physisorbed layer 220, irradiating the physisorbed layer 220with energy 224, and heating the workpiece 202 to adsorb the atoms 208 efrom dissociated molecules 208 d into the seed layer 230 and remove thephysisorbed layer 220 may be repeated one or two times in order toachieve the maximum density of the seed layer 230.

In another embodiment, the physisorbed layer 220 is preferably thinner,comprising only about 2 to 3 monolayers of the physisorbed molecules 208a. This is advantageous because the temperature does not have to belowered as much as when the physisorbed layer 220 is thick. Aphysisorbed film 220 comprising about 2 to 3 monolayers can be generatedat higher temperatures than thick condensate films or molecularcrystals, typically at temperature of about 20 to 30 K above thetemperatures needed for thick films, for example. However, when thethinner physisorbed layer 220 using the process at a higher temperaturewith 2 to 3 physisorbed monolayers is formed, the steps of lowering thetemperature, forming the physisorbed layer 220, irradiating thephysisorbed layer 220 with energy 224, and heating the workpiece 202 toadsorb the atoms 208 e from dissociated molecules 208 d into the seedlayer 230 and remove the physisorbed layer 220 may need to be repeatedmore often, e.g., two or more times, in order to achieve the maximumpossible surface coverage of chemisorbed molecules in the seed layer230.

Thus, embodiments of the invention achieve technical advantages byforming a weakly bound film of molecules, e.g., the physisorbed layer220, on top of a chemisorbed layer of the molecules, e.g., the seedlayer 210, in order to bring more dissociated molecules close to thesurface so that atoms 208 d from the dissociated molecules of thephysisorbed layer 220 can become chemisorbed atoms 208 e on the surfaceof the material layer 204, within the dense seed layer 230.

In one embodiment, the physisorbed layer 220 may comprise a materialhaving co-adsorbed molecules of the same species as chemisorbed atoms208 b in the seed layer 210. The physisorbed layer 220 may also includemolecules of a species different from the chemisorbed atoms 208 b inthis embodiment. After the manufacturing step shown in FIG. 2, theworkpiece 202 is exposed to a rate gas matrix to form the physisorbedlayer 220. The molecules of interest, e.g., those molecules of whichadditional atoms are adsorbed on the metal layer surface 204, may beembedded in the rare gas matrix, for example. Because heavy rare gaseslike krypton (Kr) or rubidium (Rb), as examples, have a highercondensation temperature than molecular oxygen or nitrogen embeddingoxygen and nitrogen, using a rare gas matrix to form the physisorbedlayer 220 allows a process of producing a physisorbed layer 220 thatbrings oxygen and nitrogen close to the metal surface 204 at highertemperatures, for example. Because rare gases only physisorb on a metalsurface 204, none of the rare gas atoms compete with thermal desorptionof the physisorbed layer 220 for an adsorption site on the metal 204surface with an oxygen or nitrogen atom produced in this layer.

In one embodiment, after the rare gas matrix is introduced to form thephysisorbed layer 220, O or N atoms are implanted into the physisorbedlayer 220. The implantation energy is preferably set such that theimplanted atoms in the physisorbed layer 220 stop in front of the metallayer 204 top surface. The workpiece 202 is then heated, producing thedense chemisorbed layer 230 comprising atoms 208 b and 208 e. In thisembodiment, preferably the physisorbed layer 220 comprises a thick raregas layer, e.g., having a thickness of about 100 nm to several 100 nm,although alternatively, the physisorbed layer 220 may comprise otherdimensions, because during the implantation process, the thickness ofthe physisorbed layer 220 will be reduced.

In another embodiment, the molecules of the physisorbed layer 220 may bepart of larger molecules, e.g., if the physisorbed layer 220 comprisesN, the physisorbed layer 220 may be formed using NH₃. The thermaldesorption temperatures of the other parts or fragments of the largermolecule may be significantly lower than the desorption temperature ofthe chemisorbed species to be adsorbed on the metal layer 204 surface,in this embodiment. This would also allow running the processesdescribed herein to produce a dense seed layer at significantly highertemperatures, e.g., at temperatures that are accessible by liquidnitrogen cooling or by cooling using Peltier elements. In the case ofoxygen, for example, adsorption of a water layer could be used, byproducing ice on the metal layer 204 surface and exposing the ice toradiation that dissociates the water bonds.

In another embodiment, the atoms 208 b in the seed layer 210 may bedifferent from the atoms 208 e in the seed layer. For example, the atoms208 b may comprise oxygen atoms and the atoms 208 e may comprisenitrogen atoms which can be produced by the method described above usingphysisorption of a nitrogen film, or nitrogen embedded in a rare gasmatrix or a NH₃ film, as examples. Alternatively, the atoms 208 b maycomprise nitrogen atoms and the atoms 208 e may comprise oxygen atoms,for example. This embodiment results in a seed layer 230 adapted to bean excellent seed layer for a second material layer 234 comprising anoxynitride film, for example.

Advantages of embodiments of the invention include providing a thinner,well defined interface region 232, e.g., having a dimension d₂, whereind₂ is thinner than d₁ of FIG. 1, between a material layer 204 and asubsequently deposited material layer 234. The seed layers 230 describedherein are very dense and thus provide an improved surface for theformation of a subsequent material layer 234, resulting in awell-defined interface region 232.

Although embodiments of the present invention and their advantages havebeen described in detail, it should be understood that various changes,substitutions and alterations can be made herein without departing fromthe spirit and scope of the invention as defined by the appended claims.For example, it will be readily understood by those skilled in the artthat many of the features, functions, processes, and materials describedherein may be varied while remaining within the scope of the presentinvention. Moreover, the scope of the present application is notintended to be limited to the particular embodiments of the process,machine, manufacture, composition of matter, means, methods and stepsdescribed in the specification. As one of ordinary skill in the art willreadily appreciate from the disclosure of the present invention,processes, machines, manufacture, compositions of matter, means,methods, or steps, presently existing or later to be developed, thatperform substantially the same function or achieve substantially thesame result as the corresponding embodiments described herein may beutilized according to the present invention. Accordingly, the appendedclaims are intended to include within their scope such processes,machines, manufacture, compositions of matter, means, methods, or steps.

1. A semiconductor device, comprising: a workpiece; a first materiallayer disposed over the workpiece, the first material layer comprising afirst number of atoms at a surface; and a seed layer disposed over thefirst material layer, the seed layer comprising a chemisorbed monolayerof a second number of atoms at the surface having a surface coverage ofat least 0.5 such that the ratio of the number of first atoms at thesurface to the number of second atoms at the surface is no more than2:1, wherein the second atoms of the seed layer comprise nitrogen. 2.The semiconductor device according to claim 1, wherein the firstmaterial layer comprises a metal layer having a top surface, the topsurface of the metal layer comprising a first number of adsorption sitesaccessible by dissociative adsorption of the second atoms of the seedlayer out of a gas phase, wherein the second atoms of the seed layeroccupy a second number of adsorption sites of the top surface of themetal layer, the second number being greater than the first number. 3.The semiconductor device according to claim 2, wherein the second numberof an adsorption sites is at least two times the first number ofadsorption sites.
 4. The semiconductor device according to claim 1,wherein the saturation coverage at the surface is about 0.67 or greater.5. The semiconductor device according to claim 1, further comprising asecond material layer disposed over the seed layer.
 6. The semiconductordevice according to claim 5, wherein the second material layer comprisesoxygen.
 7. The semiconductor device according to claim 5, wherein thefirst material layer comprises Cu, Al, Ta, Ti, W, Ru, Mo, Nb, Gd, Dy,Co, Mn, combinations, or alloys thereof.
 8. The semiconductor deviceaccording to claim 7, wherein the second material layer comprises O, N,an O-containing material, or an N-containing material.
 9. Thesemiconductor device according to claim 5, wherein the second materiallayer comprises O, N, an O-containing material, or an N-containingmaterial.
 10. The semiconductor device according to claim 5, furthercomprising an interface region disposed between the seed layer and thesecond material layer.
 11. The semiconductor device according to claim10, wherein the interface region has a thickness of about 100 nm orless.
 12. The semiconductor device according to claim 5, wherein thesecond material layer comprises nitrogen.
 13. The semiconductor deviceaccording to claim 5, wherein the second material layer comprises acombination of nitrogen and oxygen.
 14. The semiconductor deviceaccording to claim 1, wherein the second atoms of the seed layercomprise a combination of nitrogen and oxygen.
 15. The semiconductordevice according to claim 1, wherein the first material layer comprisesa metal layer having a top surface.
 16. The semiconductor deviceaccording to claim 15, wherein the top surface of the metal layercomprises a plurality of adsorption sites accessible by dissociativeadsorption of the second atoms of the seed layer out of a gas phase. 17.The semiconductor device according to claim 1, wherein the second atomsof the seed layer occupy a plurality of adsorption sites of the topsurface of the metal layer.